Container for liquid hydrocarbons

ABSTRACT

A container suitable for liquid hydrocarbons which comprises an internal pinched seam container having a hydrocarbon barrier as an inner liner. The container is prepared by releasably attaching first and second curable flexible sheets over the apertures of first and second concave molds, shaping the sheets by applying a pressure differential between the surface of each sheet facing its associated mold; after shaping the first sheet, providing an aperture therein through an aperture in the corresponding mold; adhering the peripheries of the two sheets together, before or after shaping the first sheet, and providing an opening in one of the sheets; curing the sheets after shaping to form a pinched seam container; removing the container from the molds; turning the container inside out through the provided opening therein; and sealing the said provided opening.

Robinson [111 3,755,040 [4 1 Aug. 28, 1973 1 CONTAINER FOR LIQUIDHYDROCARBONS [75] inventor: Keith D. Robinson, Mogadore, Ohio [73]Assignee: The Goodyear Tire & Rubber Company, Akron, Ohio [22] Filed:Apr. 15, 1971 [21] Appl. No.: 134,167

[52] US. Cl 156/242, 156/285, 156/288,

156/289, 264/250 [51] Int. Cl. B29c 1/14 [58] Field of Search 156/156,198, 242,

Primary Examiner-Ralph S. Kendall Assistant Examiner-Caleb WestonAttorney-F. W. Brunner and H. C. Young, Jr.

[57] ABSTRACT A container suitable for liquid hydrocarbons whichcomprises an internal pinched seam container having a hydrocarbonbarrier as an inner liner. The container is prepared by releasablyattaching first and second curable flexible sheets over the apertures offirst and second concave molds, shaping the sheets by applying apressure differential between the surface of each sheet facing itsassociated mold; after shaping the first sheet, providing an aperturetherein through an aperture in the corresponding mold; adhering theperipheries of the two sheets together, before or after shaping thefirst sheet, and providing an opening in one of the sheets; curing thesheets after shaping to form a pinched seam container; removing thecontainer from the molds; turning the container inside out through theprovided opening therein; and sealing the said provided opening.

4 Claims, 5 Drawing Figures llb Patented Aug. 28, 1973 3,755,040

2 Shouts-Sheet l FIG. I W5 Pmmd Aug. 28, 1973 3,755,040

2 Shoots-Sheet 2 FIG. 5

1 CONTAINER FOR LIQUID HYDROCARBONS This invention relates to acomposite structure suitable for containing liquids and to a method ofpreparing such a composite structure.

Containers having flexible walls suitable for containing liquids andparticularly for containing liquid hydrocarbons such as automobilegasoline tanks can be prepared by building the flexible structure arounda building form and then removing the building form through a hole inthe formed flexible structure. The structures also can be prepared byforming halves of a container inside a concave mold, removing the halvesfrom the mold, ane then cementing or bonding the two halves together.All of these methods present inherent commerical production difficultiesand new methods of preparing such containers are sought.

One solution has been to provide a pinch seam container prepared byvacuum shaping curable flexible sheets and bonding them together attheir seam. However, because of this construction, combined with therequirement of an inner hydrocarbon barrier liner, difficulties withseam separation can be experienced when internal pressure is applied.

Therefore, it is an object of this invention to provide an improvedcomposite structure for containing liquid hydrocarbons and a method ofpreparing such a container.

According to this invention, a container suitable for liquidhydrocarbons comprises an internal pinch seam container, having ahydrocarbon barrier layer as an inner liner prepared by the method whichcomprises releasably attaching first and second curable polymericflexible sheets over the apertures of first and second concave molds,and shaping said sheets by applying a pressure differential between thesurface of each sheet facing the associated mold and the oppositesurface of said sheet, said sheets each comprising a layer of a flexiblecurable polymeric material adhered to a layer of thickness from about0.25 mill to about mils of a hydrocarbon barrier material comprising atleast one material selected from the group consisting of nylon,polyvinylidene chloride, a copolymer prepared from any two or all threeof vinylidene chloride, vinyl chloride and acrylonitrile, or a linearpolyester derived from a dicarboxylic acid and a straight chain glycol;after shaping the first sheet, providing an aperture therein through anaperture in the corresponding mold; adhering the peripheries of saidfirst and second sheets having their flexible curable polymeric layersfacing each other, before or after shaping the first sheet and providingan opening in one of the sheets to permit inverting the preparedcontainer therethrough; curing the sheets after shaping both to form apinched seam container; removing the container so produced from thefirst and second molds, turning the container inside out; and sealingsaid provided opening in one of the sheets.

It is preferred that the said provided opening in one of the sheets isprovided by adhering the peripheries of the first and second sheetsexcept for a portion of suffi cient size to permit inverting theprepared container therethrough followed by, after curing the sheets andinverting the container inside out, sealing said unadhered portion ofthe periphery.

It is understood that the said provided opening can be sealed with avalve, patch, curable bonding cement and other similar means.

The objects and further advantages of this invention will be apparent inview of the following detailed description and drawings.

In the drawings, FIG. 1 is a cross-sectional view of a first concavemold having a first sheet of curable polymeric flexible material havinga hydrocarbon layer adhered thereto and facing the mold releasablyattached, or clamped, over its aperture. FIG. 2 is a crosssectional viewof the first concave mold having the first flexible sheet in a concaveposition on the concave surface of the mold and a second flexible sheetadhered over the aperture of first concave flexible sheet except for aportion of the periphery large enough to invert the prepared containertherethrough and with a vent pipe attached to the formed cavity betweenthe first and second sheets. FIG. 3 is a cross-sectional view of thefirst concave mold, the first sheet positioned on the concave surface ofthe first mold, a second concave mold positioned and releasably attachedby clamping over a second sheet, and the second sheet in a concaveposition on the surface of the second concave mold with its hydrocarbonbarrier layer facing the second mold. FIG. 4 is a perspective view ofthe pinched seam container removed from the molds. FIG. 5 is aperspective view of the internal pinched seam container of thisinvention having a hydrocarbon barrier inner liner formed by invertingthe container of FIG. 4 through the opening in its periphery.

Referring to the figures, a first flexible sheet 1 is providedcomprising a flexible curable polymeric material 2 such as naturalrubber, synthetic rubber, or a polyurethane and preferably a hydrocarbonresistant polymeric material such as a butadiene-acrylonitrilecopolymer, with a layer of hydrocarbon barrier material 3 adheredthereto such as nylon, polyvinylidene chloride and polyester types.

A first concave mold 4 is provided having venting tubes 5 attached andconnected to a vacuum or re duced pressure source such as a vacuum pump.On the inside surface of the mold are positioned small fibrous pads 6such as a textile fabric over the openings of the venting tubes 5 todistribute'the gas flow and thereby prevent the opening of a vent tubefrom becoming closed.

The first flexible sheet I is releasably attached to the aperture of thefirst concave mold 4 with clamps 7 to form an enclosed cavity 8 betweenthe first sheet and the first mold with the liquid hydrocarbon barrierlayer 3 adhered to the inner surface of the first flexible sheet 1.

A reduced pressureis then applied to the enclosed cavity 8 by applying avacuum through the vent tubes 5 to actuate the flexible sheet 1 inwardlytoward the surface of the first concave mold 4 and thereby form thefirst sheet in a concave position 9. The fibrous pads 6 in the concavemold covering the openings of the vent tubes 5 prevent the said openingsfrom becoming closed by the flexible sheet. It is preferred that thehydrocarbon barrier surface of the first sheet 1 contacts the surface ofthe first mold 4 and is molded or shaped thereby.

A vent tube 10 is injected through the first mold surface and firstshaped flexible sheet and preferably positioned with a sealant aroundthe vent so that any reduced pressure between the first mold surface andsheet is not substantially affected thereby.

If desired, a coating of curable cement 11 such as a rubber, epoxy, orphenolic type of bonding cement is applied around the periphery of theaperture of the concave first sheet on the surface of the curablepolymeric layer except for the portion ll-a.

A second flexible sheet 12 is adhered to the first sheet with the cementcoating 11, if desired except for portion 1 l-b, to define a cavity 13between the first and second sheets essentially enclosed by the curablepolymeric layers of the sheets and vented with the vent tube 10.

A second concave mold 14 is releasably attached with clamps 15 to thesecond sheet to form an enclosed cavity between the second sheet andsecond mold. The second mold is fitted with vents 16 with small fiberouspads placed thereover to a vacuum or reduced pressure source such as avacuum pump. A reduced pressure is applied to the cavity between thesecond sheet and second mold by attaching the vents 16 to the vacuumsource to actuate the second sheet inwardly toward the second mold toshape the second sheet in a concave position. The vent tube 10 providesan air source to allow air to enter the cavity between the sheets,thereby facil' itating the inward actuation of the second sheet andmaintaining a pressure differential between the second mold surface andthe outside surface which is the surface having the curable polymericlayer adhered thereto, of the second flexible sheet.

An insert 17 is placed between the two shaped sheets at theirperipheries at position 1 l-a and 11-h which will not tightly adhere tothe curable polymeric layer as it is cured. Altemately, the two flexiblesheets can be first shaped, with the vent tube 10 inserted through oneof theshaped sheets, and then adhered with the insert- 17 positionedtherebetween.

In this position, the molds are placed in a forced air oven and theflexible sheets and curable cement, if used, are cured, with the venttube 10 essentially equalizing the pressure inside and outside themolds, following which the molds are removed from the oven and theprepared container with its outer pinched seam is removed from themolds.

The insert 17 is removed and the container inverted through theresulting aperture. The aperture is then sealed such as by curing withthe aid of bonding cement, if desired.

In the description of the drawings, the flexible sheets were shaped byapplying a vacuum or reduced pressure to the cavity between a sheet anda mold member. As an alternative method, the sheets can be shaped byapplying a positive pressure to the cavity between the sheets throughthe vent l and allowing gas such as air to escape from the cavitiesbetween the sheets and molds 8 and 13 through the vents and 16, in theinstancewhere the sheets are adhered together prior to their shaping, toforce or actuate the sheets outwardly to the mold surfaces by theresultant pressure differential between an outer surface of a sheethaving a hydrocarbon barrier adhered thereto and a mold surface.

Various methods can be used for adhering the two sheets together.Preferably the sheets are adhered by their tack and cured although thevarious adhesives and bonding cements can be used, if desired.

The composite structure of this invention having an inner pinched seamand hydrocarbon. barrier inner liner can be used to contain varioushydrocarbons and their mixtures exemplary of which are petroleum andcoal tar distillates and various fueld such as gasoline and kerosene andvarious lubricating and fuel oils having oiling points at atmosphericpressure ranging from about l0 C. to about 400 C. and usually from about0 C. to about 150 C. Suitable hydrocarbons are saturated aliphatic,saturated cycloaliphatic, unsaturated aliphatic, unsaturatedcycloaliphatic, and aromatic hydrocarbons and mixtures of suchhydrocarbons. Representative examples of these and other varioussaturated hydrocarbons are aliphatic hydrocarbons such as the butanes,the pentanes, the hexanes, the heptanes, the octanes and the nonanes;aromatic hydrocarbons such as benzene, toluene and xylene; saturatedcycloaliphatic hydrocarbons such as cyclohexane; and various unsaturatedhydrocarbons representative of which is olefins such as the butenes, thepentenes, the hexanes, the heptenes, the octenes, and the nonenes; anddiolefins such as the butadienes, the pentadienes, isoprene, thehexadienes, the heptadienes, and the octadienes. Various mixtures ofunsaturated, saturated and aromatic hydrocarbons can also be contained.

In the practice of this invention, the flexible sheets used to preparethe composite structure comprise at least one layer of a flexiblepolymeric material having at least one layer of a hydrocarbon barriermaterial adhered thereto. Various flexible polymeric materials can beused, representative examples of which are curable flexible materialssuch as natural rubber and the various synthetic rubbers. Representativeof various synthetic rubbers are rubbery polymers of conjugated dienessuch as 1,4 addition polymers of 1,3-bi1tadiene and 1,4 additionpolymers of isoprene, the rubbery copolymers of butadiene and styrenewhich contain a major proportion of butadiene, particularly copolymersof butadiene and styrene of the hot and cold SBR type which contain from60 to about percent by weight of butadiene; rubbery copolymers ofbutadiene and acrylonitrile; butyl rubber, which is a polymerizationproduct of a major proportion of a mono olefin, such as butylene, and aminor portion of multi-olefin, such as butadiene and isoprene;copolymers of ethylene and propylene; and terpolymers of ethylene,propylene and a minor proportion of a nonconjugated diene and flexiblepolymers formed by the open ring polymerization of unsaturated alicycliccompounds having from one through three carbon-to-carbon double bonds inthe alicyclic ring such as 'polyoctenamers and polydodecenamers. It ispreferred to use a rubbery copolymer of 1,3-butadiene and acrylonitrilesuch as the type prepared by emulsion polymerization and it isparticularly desirable to use such a rubbery copolymer in admixture withfrom about 10 to about 60 parts of polyvinyl chloride per lOO parts ofcopolymer. It is understood that such polymers are compounded withvarious curing agents such as sulfur and peroxides, and withaccelerators, antioxidants, fillers, plasticizers, pigments and carbonblack.

The hydrocarbon barrier materials for the flexible sheets can be adheredto the flexible sheets by various methods well known to those skilled inthe art such as coating a flexible sheet with a solution of the barriermaterial or, preferably, by adhering a film of the barrier material tothe flexible sheet with an adhesive or bonding cement. A curable rubber,epoxy, or phenolic cement, for example, can be used. If the hydrocarbonbarrier material is applied as a solution, usually the solution containsfrom about 1 to about 70 parts by weight of the barrier material per 100parts by weight of solvent. Dilute solutions of from about 3 to about 20parts by weight of the barrier material per 100 parts of the solvent areusually preferred where the solutions are to be applied by ordinarymethods such as by brushing and by spraying. It is to be appreciatedthat if the viscosities of the solutions are high, the higherconcentrations are usually workable only with difficulty and specialprocedures must be applied, such as the use of higher temperatures andpressures above atmospheric.

Usually the layer of hydrocarbon barrier material on the flexible sheethas a thickness of from about 0.25 mil to about mils or thicker,although it is usually preferred that the layer has a thickness of fromabout 0.5 mil to about 5 mils.

Various materials can be used as hydrocarbon barrier materialsrepresentative of which are nylon, polyvinylidene chloride, copolymersof vinylidene chloride, vinyl chloride, and acrylonitrile, and certainlinear polyesters derived from dicarboxylic acids and straight chainglycols Representative barrier materials as copolymers prepared fromvinylidene chloride, vinyl chloride, and acrylonitrile are the polymerscomprising from about 50 to about 100 mole percent units derived fromvinylidene chloride, from about 0 to about 50 mole percent units derivedfrom vinyl chloride and from 0 to 50 mole percent units derived fromacrylonitrile. It is usually preferable that the polymer comprises fromabout 65 to about 85 mole percent units derived from vinylidenechloride, from about to about 35 mole percent units derived from vinylchloride, and from 15 to about 35 mole percent units derived fromacrylonitrile. A particularly desirable hydrocarbon barrier coatcomprises a copolymer of vinylidene chloride and acrylonitrile. Theproperties of these polymers vary widely depending upon the monomersused, the ratio of monomers used, polymerization conditions, and thedegree of polymerization. For example, their tensile strengths atultimate elongation can range from about 1,500 to about 40,000 poundsper square inch, their ultimate elongations can range from about 0 toabout 350 percent, their specific gravities can range from about 1.5 toabout 1.75, and their refractive indices can range from about 1.5 toabout 1.65. The polymers are usually characterized by being generallysoluble in cyclic ethers and ketones and generally insoluble inchlorinated hydrocarbons, aliphatic hydrocarbons, aromatic hydrocarbonsand alcohols.

If these polymers are applied to the flexible sheet as a solution, thepolymer is usually dissolved or dispersed in various solventsrepresentative of which are ketones and their mixtures which are liquidat about C. Representative of common ketones are acetone and methylethyl ketone. Various other liquids can be used as diluents inconjunction with such solvents which themselves are not good solventsfor the said copolymer, such as toluene and various alcohols to improvethe spraying or drying properties of the copolymers. Representativealcohols are methyl alcohol, ethyl alcohol, isopropyl alcohol, normalpropyl alcohol, isobutyl alcohol, normal butyl alcohol, the amylalcohols, the

hexyl alcohols and the heptyl alcohols.

Representative examples of barrier materials of a suitable polymericlinear ester comprises a polymeric polyester of substantially thestructure derived from the reaction of at least one dicarboxylic acidselected from the group consisting of terephthalic acid and isophthalicacid with at least one straight chain glycol of the series HO(CH,),.OH,where n" is an integer from 2 to 10 inclusive, and where the ratio ofunits of the polymer derived from terephthalic acid to the units derivedfrom isophthalic acid is from about 20:80 to 100:0. Representative ofsuitable straight chain glycols are ethylene glycol, propylene glycol,1,4-butane diol, 1,5-pentane diol, 1,6-hexane diol, 1,7-heptane diol,1,8-octane diol, 1,9-nonane diol and 1,10-decane diol. Usually ethyleneglycol, propylene glycol and 1,4- butane diol are preferred. Thegenerally preferred polymeric polyesters are polyethylene terephthalateand those having a ratio of terephthalic acid to isophthalic acid unitsof from about 50:50 to about :10. Suitable methods of preparing suchpolymers are shown in U.S. Pat. No. 2,965,613. It is also usuallydesired that the polymeric polyesters used as the hydrocarbon barriermaterials of this have an intrinsic viscosity of from about 0.4 to about0.8 and preferably from about 0.5 to about 0.7. for the purposes of thisinvention, when a polyethylene terephalate film is used, it is generallypreferred that it isan oriented, heat-set film which has been stretchedto substantially the same extent in both directions and heat-set at atemperature of from about 150 C. to about 200 C. under tension bymethods known to those skilled in the art.

The term intrinsic viscosity" as used in this specification can bedefined as:

specific viscosity +3 ln (relative viscosity) 40 where the relativeviscosity is defined as:

(solution flow time)/(solvent flow time), the specific viscosity isdefined as:

(relative viscosity 1); and c is the concentration of the solutionexpressed as grams of polymer per milliliters of solution. The intrinsicviscosity measurements are made at 30 C. with a solvent prepared bymixing phenol and symmetrical tetrachloroethylene in a weight ratio of60:40. Usually a solution concentration of about 0.5 gram of polymer per100 milliliters of solvent is used.

The nylons when used as the hydrocarbon barrier layer can be applied tothe flexible sheets as films and as solutions. Representative of thevarious nylons are the well-known polyamides referred to as nylons whichcomprise the reaction product of a linear polymerfonning compositioncontaining amide-forming groups, for example, one consisting essentiallyof bifunctional molecules each containing two reactive groups which arecomplementary to reactive groups in other molecules and which comprisecomplementary amideforrning groups. These polyamides as described above,or as otherwise identified hereinafter, can be obtained, for example, byself-polymerization of a monoaminomonocarboxylic acid or caprolactarn,particularly e -caprolactam, by reacting a diarnine with a dibasiccarboxylic acid in substantially equimolecular counts, or by reacting amonoaminomonohydric alcohol with a dibasic carboxylic acid insubstantially equimolecular amounts, it being understood that referenceherein to the amino acids, diamines, dibasic carboxylic acids, and aminoalcohols is intended to include the equivalent amide-forming derivativesof these reactants. The preferred polyamides are those having a unitlength of at least seven. A further description of the nylons is foundin US. Pat. Nos. 2,071,250, 2,071,253, 2,130,948 and 2,393,972.

The composite structure prepared by the method of this invention hasutility as a container for liquid hydrocarbons and it can beparticularly useful as a gasoline tank for vehicles such as automobiles.

The following illustrative example is set forth to further exemplify theobjects and advantages of this invention. The parts and percentages areby weight unless otherwise indicated.

EXAMPLE I Two sheets of a calendered flexible material having athickness of about 60 mils were prepared having the composition of thefollowing type and labeled as a first sheet and a second sheet.

Compound Parts Butadiene-acrylonitrile copolymer (1) 100 Zinc oxideSulfur [.5 Magnesium carbonate 2.25 Carbon black (fine thermal furnaceand HAF) 112 Dioctyl phthalate l7 Aryl-p-phenylene diamines 0.5Polyvinyl chloride resin (2) 43 Adipic acid ester plasticizer (3) 35Accelerator mixture of a benzothiazone sulfonarnide and a benzothiazoledisulfide 1.75

Total 318.0

1. obtained from The Goodyear Tire & Rubber Company, under the tradenameChemigum N-7;

2. obtained from The Goodyear Tire & Rubber Company, under the tradenamePliovic AO-3;

3. obtained from the F. M. C. Corporation, under the tradename AdipalBCA.

Tothe first and second sheets was adhered to transparent thermoplasticfilm of nylon of the nylon-6 type made from a polymer of e -caprolatumhaving a thickness of about 1 mil (obtained from The Allied ChemicalCompany, under the tradename Capran) with a curablebutadiene-acrylonitrile rubber adhesive labeled as rubber adhesive (A).The curable rubber adhesive had the following type of composition:

Compound Parts Butadiene-acrylonitrile copolymer (4) 72 Zinc oxide 3.5Sulfur I Carbon black (SRF) 21 Accelerator (a benzothiazole disulfide)0.5 Phenolic Resin 83.5 Methyl ethyl keton 549 Total 730.5

4. obtained from the B.F. Goodrich Company under the tradename l-Iycar1001.

A metal mold was prepared and divided into substantially identical firstand second concave halves which were identified at a first concave moldand a second concave mold.

The first and second concave molds were about 5-% inches deep and theirrectangular apertures measured about 40 inches by about 15 inches andwere fitted with venting tubes in the manner shown in FIGS. 1, 2 and 3.These venting tubes were connected to reduced pressure or vacuum source.The openings of these venting tubes on the inside surface of the moldswere covered with loosely woven cotton textile cloth in the manner shownin FIG. 3.

The first flexible sheet was then positioned and clamped over theaperture of the first concave mold with its barrier layer facing inwardtoward the mold to form a first cavity between the first sheet andsurface of the first mold in the manner shown in FIG. 1. The firstflexible sheet and mold were heated to about 70 C. by blowing hot air onthem to facilitate increasing the flexibility of the said flexiblesheet. A vacuum was applied to the first cavity through its ventingtubes thereby pulling the first flexible sheet into the first moldcavity with its barrier layer against the mold surface and shaping thefirst sheet to a' concave configuration.

A vent tube was then tightly positioned through the first mold andthrough the first sheet by puncturing the first sheet. The tightpositioning of this vent tube through the first mold and first sheetmaintained the reduced pressure or vacuum between the first mold andfirst sheet, thereby maintaining the concave configuration of the firstsheet.

A thin layer of the curable rubber adhesive (A) was coated onto thefirst sheet around the portion of the first sheet positioned over theperiphery of the aperture of the concave mold.

The second flexible sheet was adhered to the first sheet in the mannershown in FIG. 2 to form a pinched seam around their periphery except fora portion large enough through the prepared container can be inverted.In this portion, between the said sheets was positioned a bar of Teflon(trademark of the duPont de Nemours company), about 10 inches long witha thickness of about one-sixteenth inch for this purpose. A secondcavity was thus formed located between the two flexible sheets vented bythe vent tube inserted through the first mold and the first flexiblesheet. The first and second flexible sheets were positioned so thattheir curable polyrneric material surfaces were facing each other.

Over the second sheet was positioned and clamped the second moldsubstantially over the aperture of the first mold in the manner shown inFIG. 3 to form a third cavity between the second sheet and second mold.The first and second molds with the first and second sheets attachedtherein were heated to about 70 C. in a hot oven to increase theflexibility of the said sheets and then removed from the oven.

A reduced pressure or vacuum was applied to the third cavity through itsventing tubes, thereby pulling the second flexible sheet against thesecond mold surface and shaping the second sheet. A pressuredifferential between the second mold surface (third cavity) and outersurface of the second sheet having the hydrocarbon barrier adheredthereto (second cavity) was provided by allowing the vent tube to thesecond cavity between the first and second sheets to vent outside airinto the second cavity as the reduced pressure or vacuum was beingapplied to the third cavity.

The attached first and second mold halves with the shaped first andsecond flexible sheets therein where placed in a hot air oven at atemperature of about 120 C. for about 1-% hours to cure the flexiblesheets.

The composite structure was removed from the molds, the Teflon barremoved, and the container inverted through the opening in the peripheryin the pinched seam. The said opening was then sealed with a portion ofadhesive (A) and heat cured at about 140 C. The container having theinternal pinched seam and hydrocarbon barrier inner liner was filledwith gasoline and determined to be leak free.

Alternatively, the container could have been prepared by first shapingeach of the sheets in their molds, adhering them at their peripheries,curing with the vent being used to equalize pressure, and inverting thecontainer inside out.

The composite structure of this example was prepared by shaping flexiblesheets through the application of a pressure differential by applying areduced pressure in the first and third cavities. It is understood thatthe pressure differential can also be applied by applying a positivepressure to the second cavity.

In the method of this invention, for strengthening and barrier purposes,the flexible sheets can contain fibrous materials either of thenon-woven type or of the extensible woven type. Various fibers can beused such as nylon, cotton and cellulose derivatives, such as rayon.

While certain representative embodiments and details have been shown forthe purpose of illustrating the invention, it will be apparent to thoseskilled in this art that various changes and modifications may be madetherein without departing from the spirit or scope of the invention.

What is claimed is:

l. A method of preparing an internal pinched seam container suitable forcontaining liquid hydrocarbons which comprises releasably attachingfirst and second flexible sheets comprising a flexible curable polymericlayer and a flexible hydrocarbon barrier layer over the the apertures offirst and second concave molds, and shaping said sheets by applying apressure differential between the surface of each sheet facing theassociated mold and the opposite surface of said sheet, providing anaperture through the first shaped sheet through an aperture in thecorresponding mold; adhering the peripheries of said first and secondsheets having their flexible curable polymeric layers facing each other,be-

fore or after shaping the first sheet and providing an opening in one ofthe sheets to permit inverting the prepared container therethrough;curing the sheets after shaping both to form a flexible pinched seamcontainer; removing the container so produced from the first and secondmolds and turning the container inside out through the provided opening,where said curable polymeric layer of said flexible sheets is selectedfrom at least one of the group consisting of natural rubber, rubbery 1,4addition polymers of 1,3-butadiene, rubbery 1,4 addition polymers ofisoprene, rubbery copolymers of butadiene and styrene, rubberycopolymers of butadiene and acrylonitrile, butyl rubber, rubberycopolymers of ethylene and propylene, terpolymers of ethylene, propyleneand a minor proportion of a nonconjugated diene, and polymers formed bythe open ring polymerization of unsaturated alicyclic compounds havingfrom one through three carbon-to-carbon double bonds in the alicylicring, and where said barrier layer has a thickness of about 0.25 toabout 10 mils and comprises at least one material selected from thegroup consisting of nylon, polyvinylidene chloride, a copolymer preparedfrom any'two or all three of vinylidene chloride, vinyl chloride andacrylonitrile, or a linear polyester derived from a dicarboxylic acidand a straight chain glycol.

2. The method of claim 1 wherein said provided opening is formed byproviding an insert between a portion of the peripheries of the two saidflexible uncured sheets to which their uncured polymeric layers will nottightly adhere when cured and removing said insert after curing thesheets.

3. The method of claim 1 wherein the flexible sheet comprises a rubberycopolymer of 1,3-butadiene and acrylonitrile in admixture with fromabout 10 to about 60 parts of polyvinyl chloride per parts by weight ofsaid rubbery copolymer.

4. The method of claim 3 wherein the hydrocarbon barrier layer on theflexible sheet comprises at least one material selected from the groupconsisting of nylon, polyvinylidene chloride and a polyester having thestructure derived from at least one dicarboxylic acid selected fromterephthalic acid and isophthalic acid with at least one straight chainglycol having from two to 10 carbon atoms where the ratio of units ofthe polyester derived from terephthalic acid to isophthalic acid is fromabout 20:80 to about 100:0.

2. The method of claim 1 wherein said provided opening is formed byproviding an insert between a portion of the peripheries of the two saidflexible uncured sheets to which their uncured polymeric layers will nottightly adhere when cured and removing said insert after curing thesheets.
 3. The method of claim 1 wherein the flexible sheet comprises arubbery copolymer of 1,3-butadiene and acrylonitrile in admixture withfrom about 10 to about 60 parts of polyvinyl chloride per 100 parts byweight of said rubbery copolymer.
 4. The method of claim 3 wherein thehydrocarbon barrier layer on the flexible sheet comprises at least onematerial selected from the group consisting of nylon, polyvinylidenechloride and a polyester having the structure derived from at least onedicarboxylic acid selected from terephthalic acid and isophthalic acidwith at least one straight chain glycol having from two to 10 carbonatoms where the ratio of units of the polyester derived fromterephthalic acid to isophthalic acid is from about 20:80 to about100:0.